Fig. 5. BR-C protein is bound to the fkh locus 98 D2-3 in salivary glands of mid- and late third instar larvae. Salivary gland polytene chromosomes of puff stage (PS) 1 and 6 were immunostained with anti-BR-C antibody SA 4256 (middle panels, red) and counterstained with Hoechst 33258 (top panels, green). In the bottom panels both stains are merged. A section of the third chromosome that encompasses the fkh locus at 98 D2-3 is shown. A strong fluorescent signal is observed at this locus when the Sgs genes are active (PS1) and after cessation of Sgs gene expression (PS 6).